Method of thermoforming a plastic appliance door

ABSTRACT

A unitary plastic appliance door is produced by thermoforming an outer door panel and an inner door liner and joining them together in a unitary apparatus. The inner door liner is formed of sheet plastic on a male mold member and is then positioned over a female mold member mounted alongside the male mold member. The outer door panel is formed from a second sheet of plastic in the female mold member and then the inner door liner is registered with the formed outer door panel in the female mold member and is joined thereto to form the appliance door.

This application is a divisional of application Ser. No. 07/671,858,filed on Jun. 28, 1996, now U.S. Pat. No. 5,759,591.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to the art of household appliances and,more specifically, to a method and apparatus for thermoforming a plasticappliance door from two plastic sheets.

2. Discussion of the Prior Art

It is commonly known to produce a plastic appliance door, and inparticular, a refrigerator door by independently manufacturing thevarious components that combine to make the door and then, in a separatemanufacturing step, assembling the various components. For example, asrepresented in FIG. 1 of this application, it is common to form an outerrefrigerator door panel 5 from a single stamped sheet of metal which isfolded in order to form sides 8 and inwardly turned flanges 10. Theinner liner 13 associated with such a refrigerator door is oftenthermoformed on a male mold member. In general, such an inner liner 13is made on the male mold member because of the high draw ratios thatwould be involved with the use of a female mold member. Once the outerrefrigerator door panel 5 and the inner refrigerator door liner 13 areformed, inner liner 13 is secured to door panel 5 along flanges 10,along with an annular gasket 16, by means of a plurality of connectingstrips 18 and screws 20. A separate handle 22 is then secured to outerrefrigerator door panel 5 by means of screws 24. Outer refrigerator doorpanel 5 is also generally formed with upper and lower aligned holes 27which are adapted to receive pivot bushings 29 for mounting theassembled refrigerator door to a refrigerator cabinet. For insulationpurposes, it is also known to inject foam between refrigerator doorpanel 5 and inner liner 13 after complete assembly of the refrigeratordoor.

The manufacturing procedure associated with constructing such arefrigerator door formed from various, individually produced componentswhich are later assembled together, is inefficient. Such a process isextremely time consuming and requires various manufacturing stageswherein the individual components are made and assembled. In addition,since the outer refrigerator door panel 5 is made of metal, its outersurface must be painted for aesthetic purposes. The need for thesemultiple manufacturing stages obviously increases the overall costsassociated with manufacturing such a refrigerator door.

It has also been proposed to manufacture a hollow refrigerator doorformed entirely from plastic. Such an arrangement is generally shown inFIGS. 2, 3 a and 3 b and disclosed in U.S. Pat. No. 5,306,082. Accordingto this method of making a refrigerator door, the first step in themanufacturing process involves independently making the individualcomponents which combine to form the inner door members. As shown inFIG. 2, these inner components generally constitute opposing sidemembers 35, 37 and a plurality of shelf defining members 40-42. Ingeneral, these interior components are separately blow molded byarranging two parallel sheets of plastic between first and second moldmembers (see FIGS. 3a and 3 b), closing the mold members so as to pinchthe sheets about outer perimeters thereof and injecting air between thesheets so as to cause the sheets to expand against the mold members.Side members 35, 37 and shelf members 40-42 are formed with tabs 45which are adapted to extend within slots 48 formed in an outer doorpanel 50 that is constituted by a hollow plastic slab which is also blowmolded. In a final stage of the blow molding of the outer door panel 50,the tabs 45 provided on side members 35, 37 and shelf members 40-42 arepositioned within slots 48 such that slots 48 form about tabs 45 inorder to secure side members 35, 37 and shelf members 40-42 to outerdoor panel 50. An annular gasket 52 is then secured by means ofconnecting strips 55 and screws 57 to an outer annular flange portion 59of door panel 50. In addition, a separate handle 62 is secured to doorpanel 50 by means of screws 64.

The refrigerator door construction arrangement as represented by FIGS.2, 3 a and 3 b has several advantages over the construction arrangementrepresented in FIG. 1 and discussed above. First, the entirerefrigerator door of the FIG. 2 arrangement is formed from plastic andtherefore its desired shape can be readily varied. In addition, such amanufacturing operation does not require a subsequent painting stage forouter door panel 50. Furthermore, making the outer door panel 50 fromplastic can provide some additional heat efficiency benefits since themetal door panel of the FIG. 1 arrangement will be a better conductor ofheat into the refrigerator than the plastic door. Finally, the use ofplastic presents the ability to integrally form the outer door panelwith a handle as also proposed in the prior art and represented in FIG.4.

However, these previously proposed all-plastic refrigerator doorarrangements suffer from various drawbacks. For example, the variouscomponents which make up each of the refrigerator doors are stillseparately manufactured and subsequently assembled. As indicated above,this is considered inefficient as it adds to the manufacturing time andcost associated with making such doors. Furthermore, the knownall-plastic refrigerator door arrangements are generally notaesthetically appealing since the interconnection between the variouscomponents are often noticeably visible and there will be a pinch linewhere the mold halves close. Finally, although forming an outer doorpanel of plastic with an integrally formed handle reduces manufacturingcosts associated with the outer door panel and is rather aestheticallyappealing, the prior proposed system as represented in FIG. 4 forms thehandle, generally indicated in 68, by creating a recess in the frontsurface 71 of the outer door panel 74 which inherently reduces theenergy efficiency of the refrigerator door as a whole due to its reducedthickness.

Therefore, there exists a need in the art for a plastic refrigeratordoor which can be produced in a minimum number of manufacturing stagesso as to reduce the manufacturing costs associated with the refrigeratordoor. In addition, there exists a need in the art for a all-plasticrefrigerator door and method of making the same wherein the energyefficiency associated with the refrigerator door is maintained orincreased. Finally, there exists a need in the art for an aestheticallyappealing plastic refrigerator door.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved methodand apparatus for thermoforming an all-plastic appliance door whichminimizes the manufacturing stages and associated costs of producingsuch a door.

It is another object of the invention to provide an improvedthermoforming apparatus wherein the male and female mold members forforming the inner and outer door panels are both located on a firstmovable platen.

It is a further object of the present invention to provide an improvedmethod of thermoforming wherein an exterior plug assist is locatedwithin a shuttle box mounted on a second movable platen.

It is a still further object of the invention to provide an improvedmethod of thermoforming wherein the shuttle box and exterior plug assistare mounted for shuttle movement between the male and female molds.

These and other objects of the present invention are achieved by amethod and apparatus for thermoforming an appliance door includingproviding a male mold member shaped to the contour of an inner doorliner being formed and providing a female mold member shaped to thecontour of an outer door panel being formed. Also provided is a movableshuttle box including a first plug assist, the shuttle box and firstplug assist being moveable into registry with either of the male andfemale mold members. Further to this method, a first plastic sheet ismoved into position with respect to the male mold member andsubsequently the shuttle box and first plug assist are placed intocontact with the first plastic sheet and into registry with the malemold member while applying heat and vacuum to the first plastic sheet toform the inner door liner. The shuttle box and first plug assist arethen withdrawn from the male mold member with the door liner attachedand the shuttle box and first plug assist are moved into a verticallyaligned position with respect to the female mold member. A second plugassist, which cooperates with the female mold member, is moved into avertical alignment position with respect to the female mold member andthe female mold member is moved into contact with one side of the secondplastic sheet. The second plug assist is actuated into contact with theopposite side of the second plastic sheet, into registry with the femalemold member and heat and vacuum are applied to the second plastic sheetto form the outer appliance door panel. The second plug assist isretracted from the formed door panel which is retained within the femalemold member and the shuttle box and first plug assist with attached doorliner are moved into registry with the female mold member and attacheddoor panel. Finally, the door liner and outer door panel are heat sealedtogether along respective peripheral edges thereof to form an appliancedoor.

Other objects, features and advantages of the invention should becomeapparent from the following detailed description of a preferredembodiment thereof when taken in conjunction with the drawings whereinlike reference numerals refer to corresponding parts in the severalviews.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of a refrigerator door constructed inaccordance with the prior art.

FIG. 2 is an exploded view of another refrigerator door constructed inaccordance with the prior art.

FIG. 3a is a cross-sectional view of a molding device used to make therefrigerator door of FIG. 2 in its open state.

FIG. 3b is a cross-sectional view of a molding device of FIG. 3a in itsclosed state.

FIG. 4 is a perspective view of another plastic refrigerator doorconstructed in accordance with the prior art.

FIG. 5 is a perspective view of a refrigerator incorporating a unitaryall-plastic refrigerator door constructed in accordance with the presentinvention.

FIG. 6 is a schematic plan view of the thermoforming process layout forthermoforming a unitary plastic refrigerator door.

FIG. 7 illustrates the initial stage in the method of forming the innerliner of the refrigerator door shown in FIG. 5.

FIG. 8 is a view of the molding apparatus of FIG. 7 in another stage offorming the inner liner.

FIG. 9 is a view of the molding apparatus of FIG. 8 in a subsequentmanufacturing stage of forming the inner liner.

FIG. 10 is a view of the molding apparatus of FIG. 8 upon completion offorming the inner liner.

FIG. 11 is a view of the initial stage in the process of forming theouter door panel of the refrigerator door shown in FIG. 5.

FIG. 12 is a view of the molding apparatus utilized in accordance withthe present invention in a subsequent outer door panel forming stage.

FIG. 13 is a view of the molding apparatus in another stage of formingthe outer door panel.

FIG. 14 is a view showing the posture of the apparatus just prior tojoining the inner liner and outer door panel.

FIG. 15 is a view depicting the step of joining the inner liner andouter door panel

FIG. 16 is a view of the forming apparatus in an open state followingcompletion of the forming operation.

FIG. 17 is an enlarged sectional view of a portion of the formedrefrigerator door of the present invention showing in detail thetrimming rule in the female mold member and the back-up plate in theshuttle box.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 5 schematically depicts a refrigerator 80 constructed in accordancewith the present invention. Refrigerator 80 generally includes a cabinet83 having various compartments (not shown) formed therein that areselectively closed off by a freezer compartment door 86 and arefrigerator compartment door 88. Refrigerator 80 further includes akick plate 90. It should be noted that the structure of cabinet 83 andkick plate 90 are not considered part of the present invention andtherefore will not be further discussed herein. In addition, it shouldbe noted that, although particular reference will be made torefrigerator compartment door 88 in describing the plastic refrigeratordoor and its method of manufacture in accordance with the presentinvention, it should be readily understood that the term “refrigeratordoor” refers to either a freezer compartment door or a refrigeratorcompartment door. The present invention is equally applicable to doorsfor combination refrigerator/freezers or dedicated refrigerator orfreezer units.

Refrigerator compartment door 88 includes an outer refrigerator doorpanel 91 and an inner refrigerator door liner (not shown in FIG. 5) aswill be more fully discussed below. Outer refrigerator door panel 91includes an outer wall portion 92 having an associated surface 93 and aninwardly turned annular sidewall 94. Outer wall portion 92 includes athickened portion 95 that projects slightly outwardly from surface 93. Aplateau section 99 includes left and right recess defining handles 103,104 that are defined between a central plateau section 107 and left andright upstanding, thickened end portions 110, 111 of thickened portion95. As is commonly known in the art, refrigerator door panel 91 can bepivotally mounted about a vertical axis to either the left or right handsides of cabinet 83. For this reason, the left and right halves ofrefrigerator door panel 91 are preferably symmetrically formed with theleft and right recess defining handles 103, 104. However, it should bereadily understood that refrigerator door panel 91 could be designed foruse in connection with a refrigerator 80 having a predetermined dooropening side wherein only one handle may be required. In addition,although thickened portion 95 is depicted in the preferred embodiment ofFIG. 5 to be located at the upmost portion of refrigerator door panel91, it should be readily understood that thickened portion 95 could berepositioned in order to locate handles 103 and 104 at a desiredlocation and orientation. Since thickened portion 95 projects outwardlyfrom surface 93, the formation of handles 103 and 104 do not detractfrom the overall energy efficiency of refrigerator door panel 91. Inother words, the heat transfer characteristics associated withrefrigerator door panel 91 are only increased by the presence ofthickened portion 95 as opposed to the inherent decrease in the desiredheat transfer characteristics that could be present if a handle wasdefined by a recess formed inward of surface 93.

In accordance with the preferred embodiment, refrigerator compartmentdoor 88 is made by a thermoforming process which advantageously enablesthe particular shape of refrigerator door panel 91 to be readily alteredif desired. In addition, in accordance with the present method ofthermoforming a refrigerator door, refrigerator compartment door 88 canbe advantageously made from two plastic sheets utilizing a singlemolding apparatus with the inner door liner 130 associated withrefrigerator compartment door 88 being formed on a male mold member asnow will be discussed with reference to FIGS. 6-17.

FIG. 6 shows in schematic form a plan view of the machine set-up forthermoforming the refrigerator door 88 of FIG. 5. A carouseltransportation member 100 is rotatable about an axis 98 between aloading-unloading station 101, a preheat oven 102, a final heat oven 105and a forming station 106 housing the forming machine or press 114. Thetransportation member 100 is circular in shape and is divided intoquadrants which alternately mount and transport or shuttle first andsecond plastic sheets 149 and 150 for rotational movement through theforming station 106. The machine set-up for thermoforming could belinear rather than the preferred carousel arrangement shown herein. Suchan arrangement is described in U.S. Pat. No. 5,533,511, issued Jul. 9,1996 and assigned to the assignee of the present application. Thislinear arrangement is hereby incorporated by reference.

As best shown in FIGS. 7-17, the forming station 106 includes a machineor press 114 that includes upper and lower movable platens 115 and 116which in operation move toward and away from each other. The upper andlower platens 115 and 116 are each equipped with stationary stops 119and 120 that contact each other at predetermined stages when the tool114 is operated and assure alignment of the platens 115 and 116. Theupper platen 115 has at least four lock arms 121 which mate with atleast four corresponding lower platen lock arms 122 in order to lock theupper and lower platens 115 and 116 together. In the preferredembodiment, the upper and lower lock arms 121 and 122 are engaged with abayonet locking arrangement.

As further shown in FIG. 7, the lower platen has a mold mounting plate123 mounted on a plurality of pressureizable forming air bags 124 andlocated by guide pins 125 at each corner of the mounting plate 123. Inthe preferred embodiment, laterally spaced apart male and female molds126 and 129 are attached to the mounting plate 123 in a substantiallyside-by-side arrangement. The male mold 126 is used for forming theinner door liner 130 of the refrigerator or appliance door 88 and thefemale mold 129 is used for forming the outer door panel 91 of arefrigerator or appliance door 88.

The upper platen 115 includes a movable first plug assist member 131which faces the male and female molds 126 and 129 that are attached tothe lower platen 116. The first plug assist member 131 can be movedlaterally between the male and female molds 126 and 129 for verticalalignment therewith by means of a drive system 132 driven, in thisembodiment, by an electric motor 133. The first plug assist member 131has a plurality of surfaces 134 that cooperate with the opposed surfacesof the male mold 126 to assist in the forming of the inner door liner130 by pushing the plastic sheet material into conformity with thesurface of male mold member 126.

The first plug assist member 131 is enclosed in a box-like structure orshuttle box 136 that forms a substantially air tight pressureizableenclosure when engaged with a sheet of plastic and in registry witheither the male or female molds 126 and 129. The box-like structure orshuttle box 136 further includes a mold trimming pinch surface orback-up plate 139 extending around the full perimeter of the shuttle box136. The female mold 129 has an in-mold steel trimming rule 140 whichlikewise extends around its outer perimeter and is cooperable with thepinch surface 139 of the shuttle box 136 for trimming the joint edge ofthe two panels that form the refrigerator or appliance door 88 as willbe further discussed with respect to FIG. 17.

Located adjacent the position of the female mold 129 and horizontallymovable into and out of proximity therewith, is a second plug assistmember 141. The second plug assist member 141 has a plurality of movablesurfaces 142 operated by pneumatic rams 143 that aid in forming theshape of the outer door panel 91. It is anticipated that hydraulic ramscould be substituted for the pnuematic rams 143.

As still further shown in FIGS. 7 and 11, the transportation member 100includes a rail arrangement 144 between the upper and lower platens 115and 116 for carrying sheet support members 145 and 146 that shuttle ortransport plastic sheets 149 and 150 into position above the male andfemale molds 126 and 129 respectively.

Referring again to FIG. 7, the method of forming a two-panel plasticrefrigerator or appliance door 88 will be described. First, the shuttlebox 136 and first plug assist member 131 are aligned vertically abovethe male mold 126. With the upper and lower platens 115 and 116separated, a first plastic sheet 149 mounted on a first sheet supportmember 145 is shuttled or moved from a final heat oven 105 into positionover the male mold 126 by way of the rail arrangement 144. Next, asshown in FIG. 8, the lower platen 116 is moved upwardly so that dikeforming portions 151 of the male mold 126 will engage and place tensionon the first plastic sheet 149. At this point, the upper platen 115 ismoved downwardly toward the lower platen 116 placing the shuttle box 136housing the first plug assist member 131 into contact with the firstplastic sheet 149 and into registry with the male mold 126. The varioussurfaces 134 of the first plug assist member 131 engage the uppersurface of the first sheet of plastic 149 and push the plastic sheet 149into the corners of the male mold 126 to conform the plastic sheet 149to the surface of the male mold 126 as best shown in FIG. 9. Atapproximately the same time, a vacuum is applied to the lower surface ofthe first plastic sheet 149 through the male mold 126. As previouslydiscussed, the shuttle box 136 can be pressurized and thus pressure maybe applied to the inner surface of the plastic sheet 149 by pressurizingthe shuttle box 136. Thus, the first plastic sheet 149 has been formedinto an inner door liner 130. The formed inner door liner 130 is thenclamped to the pressurized shuttle box 136.

Once the inner door liner 130 has been formed in this manner, the lowerplaten 116 is retracted. The first sheet support member 145 is thenreleased from the formed inner door liner 130 by unclamping the clampframes 157 as shown in FIG. 10 and the inner door liner 130 will remainclamped to the shuttle box 136. The upper and lower platens 115 and 116are separated from each other as shown in FIG. 10 with the inner doorliner 130 held by picker devices (not shown) that engage with undercutareas of the inner door liner 130 and raise the inner door liner 130with the upper platen 115.

There is shown schematically on the sides of the shuttle box 136 in FIG.10, heaters 147 which may be attached to the shuttle box 136 and placedadjacent the peripheral edge 158 of the formed inner door liner 130 forapplying heat to the inner door liner 130 for maintaining apredetermined material temperature around the peripheral edge 158. Thisheater 147 may be of any well known type such as calrod, ceramic orquartz.

Next, the shuttle box 136 and attached inner door liner 130 are drivenor shuttled horizontally to a position vertically aligned over the topof the female mold 129. Simultaneously, as shown in FIG. 11, a secondplastic sheet 150 is shuttled or transported into position over thefemale mold 129 by a second sheet support member 146. Also at this time,the second plug assist member 141 is moved into position over the top ofthe second plastic sheet 150 and into registration with the cavity 152of the female mold 129, as shown in FIG. 12.

As is apparent in FIG. 12, the lower platen 116 of the press 114 is nowmoved upwardly to move the female mold 129 into contact with the bottomof the second plastic sheet 150 to place slight tension on the plasticsheet 150. Next, heat is applied to second plastic sheet 150 and asshown in FIG. 13, a vacuum is applied to the lower surface of the secondplastic sheet 150 through the female mold member 129 to conform thesecond plastic sheet 150 to the cavity 152 of the female mold 129 whileat the same time, the second plug assist member 141 is actuated todeploy the movable surfaces 142 for assisting in forming at least theside wall portions of the outer door panel 91. Thus, the second plasticsheet 150 has been formed into an outer door panel 91. Once the outerdoor panel 91 has been formed onto the female mold member 129, thesecond plug assist member 141 is quickly retracted as shown in FIG. 14and is backed away as shown in FIG. 7 and into the plane of FIG. 14.

With the second plug assist member 141 out of the way and the heaters147 retracted, the shuttle box 136 including the first plug assistmember 131 with the attached inner door liner 130 is lowered into aregistry position on top of the formed outer door panel 91 that has beenretained within the female mold 129 by lowering the upper platen 115 ofthe press 114 as shown in FIG. 15. Once this is done and registry isaccomplished so that the inner door liner 130 is engaged with the outerdoor panel 91, the upper and lower lock arms 121 and 122 are engaged andlocked and the air bags 124 are inflated to move the mold mounting plate123 slightly upward on guide pins 125 to squeeze the inner door liner130 and outer door panel 91 together around their periphery. At thistime, pressure may be applied to the shuttle box 136 by injecting airthrough air ports 138 while injecting air through blow pin 137 into thespace between the inner door liner 130 and the outer door panel 91 topressure form the exterior. Differently stated, with the application ofheat, the inturned edge 153 of inner door liner 130 is joined or fusedto the inwardly turned annular sidewall portion 94 of outer door panel91, see FIGS. 15 and 17. Once these two portions of refrigerator door 88are joined, air pressure can be immediately applied through the blow pin137 into the interior of the newly formed refrigerator compartment door88 and into the shuttle box 136 through air ports 138 to enhance thedetails of outer door panel 91 with the air pressure within the shuttlebox 136 and within the refrigerator door 88 being equal. The steel rule140 in the mold 129 will trim the outer perimeter edge of the door 88.As best shown in the cross section of FIG. 17, the steel rule 140 has aknife edge 148 which engages with the back-up plate or pinch surface 139for trimming the refrigerator door 88.

After this joining and rough trimming operation is complete, the upperand lower platens 115 and 116 are separated as shown in FIG. 16 and theshuttle box clamps (not shown) are released leaving the door 88 on thesecond sheet support member 146. The knife edge 148 is interrupted atseveral preselected locations around the peripheral edge 158 so thatduring trimming a plurality of tabs (not shown) will remain to permitthe completed refrigerator door 88 to move with the second supportmember 146 by way of the trimmed excess material. The completedrefrigerator door 88 is shuttled or transported out from between theupper and lower platens 115 and 116 and toward unloading station 101where an operator can quickly cut away the tabs and remove theperipheral excess plastic. The shuttle box 136 is now shuttled ortransported back into the initial position over the male mold member 126and the process is repeated.

The interconnection between inturned edge 153 of inner refrigerator doorliner 130 and inwardly turned annular sidewall 94 of outer refrigeratordoor panel 91 is perhaps best shown in the enlarged view of FIG. 17.Once the thermoformed refrigerator door 88 is removed from the formingarea, this joined area between inner refrigerator door liner 130 andouter refrigerator door panel 91 may be rounded or beveled if desired.When refrigerator door 88 is assembled to the cabinet 83, the trim line154 is hidden from frontal and side view and a seam defined by thejoined area is located between annular side wall portion 94 and dikeportion 155 and extends substantially perpendicular to an outer wallportion of door panel 91 as clearly shown in FIG. 17.

FIG. 17 also illustrates that, in accordance with the preferredembodiment of the invention, the internal chamber 156 defined betweenouter refrigerator door panel 91 and inner refrigerator door liner 130can be filled with a heat insulating material. In the preferredembodiment, foam 159 is injected into internal chamber 156 and extendseven into dike portion 155 in order to provide, in addition to enhancedthermal specifications for refrigerator compartment door 88, additionalstructural rigidity without significantly increasing the weight ofrefrigerator compartment door 88.

From the above discussion, it should be readily apparent that forming anall-plastic refrigerator door in accordance with the present inventionminimizes the number of manufacturing steps necessary and results inreduced manufacturing costs. In addition, since the refrigerator door iscompletely made from plastic, it will be a more durable thanconventional metal/plastic doors and can be more versatile in design.One of the key benefits to the manufacturing process is that the doorcan be manufactured such that the joining seam whereat the outer doorpanel meets the inner liner faces toward the inside of the refrigerator.Due to this positioning of the seam, a door gasket can be advantageouslydesigned to cover the seam so as to provide an extremely aestheticallyappealing overall assembly.

A gasket arrangement for use with the refrigerator compartment door 88as shown herein is described, for example, in drawing FIGS. 14 and 15and specification at column 8 of U.S. Pat. No. 5,533,311 issued Jul. 9,1996 and assigned to the assignee of the present application. Thisgasket arrangement is hereby incorporated by reference.

Although various materials could be utilized in connection with thepresent invention to form the refrigerator door, in the preferredembodiment, outer refrigerator door panel 91 is formed from a sheet of ahigh impact polystyrene layer of approximately 92-97 mils in thicknesshaving an acrylic cap layer of polymethylmethacrylate in the order of3-8 mils. The refrigerator door liner 130 is preferably formed of highimpact polystyrene. In addition, a foam barrier layer of a styrenicalloy may be used on the inside surfaces of both the outer refrigeratordoor panel 91 and the inner refrigerator door liner 130 when certaincorrosive foams are injected within internal chamber 156. It is alsopossible to use polyvinylchloride as the material for either of thesecomponents. If polyvinylchloride is utilized, no cap layer or foambarrier will be necessary. However, the use of the polystyrene over thepolyvinylchloride is preferred based on cost factors. Instead of thepolymethylmethacrylate used for the cap layer, it is also possible toutilize styrenemethylmethacrylate.

As indicated above, the refrigerator door constructed in accordance withthe invention will be more energy efficient than conventional doorsutilizing metal panels which inherently conduct more heat into the unit.This efficiency characteristic is further enhanced by locating thethickened portion of the door that contains the handles closer to theperiphery of the door than to the dike. Obviously, the plastic alsoprovides a corrosion resistant door that does not require painting.

It is envisioned that the sequence of various steps described forforming the refrigerator door 88 can be modified. For example, the stepof moving the shuttle box 136 from being vertically aligned with themale mold member 126 and attached door liner 130 to a positionvertically aligned with the female mold member 129 may be done after thesecond plug assist member 141 and the female mold member 129 have formedthe outer door panel 91. Also, as discussed herein, the shuttle box 136does not have to be pressurized and it is not always necessary to injectair into the internal chamber 156 when joining the inner door liner 130to the outer door panel 91. Other possible changes in the sequence ofsteps will be apparent to persons skilled in the art.

Although described with respect to a preferred embodiment of theinvention, it should be readily understood that various changes and/ormodification can be made to the present invention without departing fromthe spirit thereof In general, the invention is only intended to belimited by the scope of the following claims.

What is claimed is:
 1. A method of thermoforming an appliance doorcomprising: providing a male mold member shaped to the contour of aninner door liner to be formed; providing a female mold member shaped tothe contour of an outer door panel to be formed; providing a movableshuttle box including a first plug assist, the shuttle box and firstplug assist being moveable into registry with either of the male andfemale mold members; moving a first plastic sheet into position over themale mold member; placing the shuttle box and first plug assist intocontact with the first plastic sheet and into registry with the malemold member while applying heat and vacuum to the first plastic sheet todraw the first plastic sheet against the male mold member to therebyform the inner door liner, withdrawing the shuttle box and first plugassist with the door liner attached thereto from the male mold member;moving the shuttle box and first plug assist with the door linerattached thereto into a vertically aligned position with respect to thefemale mold member; moving a second plastic sheet into position withrespect to the female mold member; providing a second plug assist forcooperation with the female mold member; moving the female mold memberinto contact with one side of the second plastic sheet; actuating thesecond plug assist into contact with a side of the second plastic sheetthat is opposite the side of the second plastic sheet in contact withthe female mold member, into registry with the female mold member andapplying heat and vacuum to the second plastic sheet to draw the secondplastic sheet against the female mold member to thereby form the outerdoor panel; retracting the second plug assist from the outer door panelretained within the female mold member; moving the shuttle box and firstplug assist with the inner door liner attached thereto into registrywith the female mold member with the outer door panel retained thereinand heat sealing the inner door liner and the outer door panel togetheralong respective peripheral edges thereof to form the appliance door;and separating the shuttle box including the first plug assist andfemale mold member to allow for removal of the appliance door.
 2. Themethod of thermoforming an appliance door according to claim 1, furthercomprising mounting the male and female mold members in a side-by-sidearrangement.
 3. The method of thermoforming an appliance door accordingto claim 1, including the step of applying heat to the peripheral edgeof the inner door liner to maintain the peripheral edge at apredetermined temperature.
 4. The method of thermoforming an appliancedoor according to claim 1, and further including the step ofpressurizing the inner door liner to enhance the features thereof. 5.The method of thermoforming an appliance door according to claim 1,including the step of pressurizing the shuttle box and the interior ofthe appliance door to further define the outer door panel.
 6. The methodof thermoforming an appliance door according to claim 1, includingremoving the completed appliance door.
 7. The method of thermoforming anappliance door according to claim 1, including injecting an insulationmaterial between the inner door liner and the outer door panel of theappliance door.